If you can access one folder on W7 but not another, you can pretty much rule out TCP/IP, name resolution and firewall/security apps causes. Odds are it's a permission problem -- remember both CIFS (sharing) and NTFS permissions are involved.I'm also thinking that I might have buggered up my smp2 install by changing ownership from admin to my user (still full admin rights).
If you're *not* accessing the shares with authenticated logon (using same passworded account on both client and server), then "Forced Guest" mode is in effect, that mean the client (XP in this case) accesses the W7 shared folders using the Guest account, and the shared folder needs to have the read/write CIFS *and* NTFS permission for "Everyone" group.
With Vista and W7 MSFT have made it difficult to add the "Everyone" permission for the core system folders, hence you have to install programs that need to be LAN accessible in %userprofile% or other non-system folders. (Personally I use an "apps" folder under root.)
The way around this is to use authenticated logon. If you use the same user account on both the client and the server (that account must have a password), then that account's credentials are used for accessing the shares instead of "Forced Guest".
In order to troubleshoot NTFS permission problems in LAN sharing, I'll need to know what account you're using in the client (XP) and the ACL of the shared folder. You can use XCACLS from the CMD console to get that folder's ACL.
W7's homegroup does not work with XP.I even went so far as to turn off the "let windows manage my homegroup settings" to see if that was the issue...